The present invention relates to a fluorescent color conversion film for absorbing light, which is emitted from a light-emitting element in the near ultraviolet to visible range, and converting it to visible light of a different wavelength. The present invention also relates to a fluorescent color conversion filter using this fluorescent color conversion film, and to an organic light-emitting device equipped with this fluorescent color conversion filter. These fluorescent color conversion film, fluorescent color conversion filter, and organic light-emitting device are well suited for use in personal and industrial display devices, such as self-light-emitting type multi-color or full color displays, display panels, and backlights.
With increasing demand for a flat panel display instead of a conventional cathode ray tube, there has been much effort towards the development and application of various display devices. An electroluminescent device (henceforth referred to as a light emitting device) is a result of this demand. It has been gathering interest particularly because it is an all solid state light-emitting device having a high resolution and high visibility that other displays do not have.
As a method for multi-color or full colorization of a light-emitting device for use in a flat panel display, there are methods of separated arrangement of light-emitting elements of three primary colors of red, blue, green in a matrix and emitting each of these colors (disclosed in Japanese Laid-Open Patent Number 57-157487, Japanese Laid-Open Patent Number 58-147989, Japanese Laid-Open Number 3-214593). When colorizing using organic light-emitting elements, the three types of light-emitting materials for RGB must be arranged in a highly detailed matrix. This is technically difficult and cannot be manufactured cheaply. Furthermore, because the three types of light-emitting materials have differing lifespans, over time, deviation of chromaticity can arise.
Furthermore, methods, wherein: the three primary colors are transmitted using color filters on a backlight that emits white light (Japanese Laid Open Patent Number 1-315988, Japanese Laid Open Patent Number 2-273496, Japanese Laid Open Patent Number 3-194895), are also known. In order to obtain a RGB with a high luminance, a white light with a long life and high luminance is necessary, however, currently, such an organic light-emitting element has not been achieved.
A method, wherein: the luminescence from a light-emitting element is absorbed by fluorescent elements which have a separated arrangement in a plane, and from each of the fluorescent elements, fluorescent light of multiple colors is emitted (disclosed in Japanese Laid Open Patent Number 3-152897), is also known. Using fluorescent elements, this method emits fluorescence of multiple colors from a light-emitting element. This method has been applied to CRT and plasma displays.
In recent years, there has been disclosed a color conversion method, wherein fluorescent material, which can emit fluorescent light in the visible range by absorbing light in the emitted range of an organic light-emitting element, is used as a filter (Japanese Laid Open Patent Number 3-152897, Japanese Laid Open Patent Number 5-258860). Because the emitted color of the organic light-emitting element is not limited to white light, an organic light-emitting element with a higher luminance can be used as the light source. A color conversion method using an organic light-emitting element with a blue luminescence (disclosed in Japanese Laid Open Patent Number 3-152987, Japanese Laid-Open Patent Number 8-286033, Japanese Laid-Open Patent Number 9-208944) can convert the wavelength of blue light to green light or red light. With highly detailed patterning of the fluorescent color conversion film containing this kind of fluorescent dye, a full color luminescent display can be constructed even when a weak energy ray, such as near ultraviolet to visible light, of a light-emitting element is used. With regard to methods for patterning of the fluorescent color conversion film, there are (1) as with inorganic fluorescent elements, methods, wherein after dispersing fluorescent dye in a liquid resist (photoreactive polymer) and creating a film with this by spin coat method or the like, patterning is conducted by a photolithography method (Japanese Laid Open Patent Number 5-198921, Japanese Laid-Open Patent Number 5-258860), and (2) a method, wherein: fluorescent dye or fluorescent pigment is dispersed in a basic binder, and this is etched with an acidic aqueous solution (disclosed in Japanese Laid Open Patent Number 9-208944).
However, with the method of patterning by the photolithography method of the above (1), the organic fluorescent dye could decompose or become quenched. In the photolithography process of the liquid resist in which the organic fluorescent dye is dispersed, these problems are a result of attack by radicals generated from photo polymerization initiators and/or thermo-polymerization initiators (hardening agents) in the resist, or from attack by reactive multifunctional monomer growth radicals from reactive multifunctional monomers and oligomers.
Furthermore, with the method of etching by an acidic aqueous solution of the above (2), patterning is conducted after coating the resist on top of a fluorescent color conversion film, which comprises a basic binder. As a result, there are many steps in the manufacturing process. Furthermore, there are problems such as pattern thinning due to side etching, and the like. As a result, an adequate solution to the problems has not been achieved.
It is an object of the present invention to provide a fluorescent color conversion filter and an organic light-emitting device equipped with this fluorescent color conversion filter which overcomes the foregoing problems.
More specifically, it is an object of the present invention to provide a fluorescent color conversion filter and an organic light emitting device equipped with this fluorescent color conversion filter in which the fluorescent color conversion filter is manufactured using a photolithography process and in which the decomposition and quenching of the fluorescent coloring matter resulting from attacks from radicals generated from polymerization initiators and/or growth radicals of reactive multifunctional monomers are suppressed.
The first embodiment of the present invention is a fluorescent color conversion film, in a fluorescent color conversion filter, comprising an organic fluorescent dye which absorbs light obtained from a light-emitting element in the near ultraviolet to visible range and emits a different visible light and a matrix resin which bears this organic fluorescent dye, herein the organic fluorescent dye is an immobilized organic fluorescent dye enclosed by a cyclodextrin derivative represented by the following general formula (I). 
wherein n is an integer from 4 to 10, each of R1xcx9cR5 are selected independently from he group consisting of a hydrogen atom, a carboxyl group, a hydroxyl group, and an C1 to C6 alkyl group.
The second embodiment of the present invention is a fluorescent color conversion film as described in the first embodiment, wherein n is an integer from 4 to6.
The third embodiment of the present invention is a fluorescent color conversion filter comprising: a fluorescent color conversion film as described in the first or second embodiments, and a substrate.
The fourth embodiment of the present invention is an organic light-emitting device, comprising: a fluorescent color conversion filter as described in the third embodiment, and an organic light-emitting element.
An enclosure complex is a complex in which a guest molecule is captured inside an open space (henceforth referred to as inner space) formed in a host molecule. From the shape of the open space formed by the host molecule in a crystal, they are classified as cylindrical or basket-shaped. Various host molecules are known. Among these, cyclodextrin is well known as a host molecule. Cyclodextrin is a ring oligomer of glucose and has the following properties: large amounts of the pure compound can be obtained easily, the size of the inner space can be chosen by the number of glucoses, and various chemical modifications are possible. Cyclodextrin is classified as cylindrical. Because hydroxyl groups and other hydrophilic residual groups extend outward on the outside of this cylinder, the inner space has a relatively low polarity and is very hydrophobic. As a result, hydrophobic substitution groups such as phenyl groups and the like are easily taken into the inner space, and an enclosure complex is formed readily. Furthermore, because the movement of the guest molecule, which has entered in the inner space, is constrained, the conformation is limited. With respect to organic dye, it has been reported by I. R. Politzer et al that rhodamine 6G and rhodamine B, which are xanthene dyes, are enclosed by cyclodextrin, and the absorption spectrum and fluorescence spectrum become altered (Chemical Physics Letters, 159, 258 (1989)).
As described above, when patterning the liquid resist in which organic fluorescent dye is dispersed using a photolithography method, there was a problem of a decrease in color conversion efficiency due to the decomposition and/or quenching of the organic fluorescent dye because of attacks by radicals generated from photo polymerization initiators and/or thermo-polymerization initiators or from growth radicals generated from reactive multifunctional monomers and oligomers.
After intensive research by the present inventors, it was found that the enclosure of organic fluorescent dyes by the addition of cyclodextrin derivatives has a large effect in improving the resistance to the lithography process. In other words, by adding a cyclodextrin derivative which forms an enclosure complex, the organic fluorescent dye and cyclodextrin derivative form an enclosure complex. Because the cyclodextrin as the host molecule acts as a protective wall against the attacks by radicals on the organic fluorescent dye, it is thought that this enclosure complex can suppress the decomposition and quenching of the organic fluorescent dye.
The present invention is based on these discoveries. With the fluorescent color conversion filter equipped with the organic fluorescent dye and a matrix resin which bears this organic fluorescent dye, by having the organic fluorescent dye enclosed using the cyclodextrin derivative represented by the above general formula (I), the decomposition and quenching of the fluorescent dye during the photolithography process can be suppressed. A fluorescent color conversion filter and an organic light-emitting device equipped with this fluorescent color conversion filter that is highly detailed and has a high color conversion efficiency can be easily obtained. Furthermore, when trying to achieve an organic light-emitting device which emits light of the same luminance, by using a fluorescent filter with a high color conversion efficiency, the luminance of the organic light-emitting element can be reduced, and therefore, the driving voltage can be reduced.
The above, and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.